The present invention relates to welding of thermoplastic parts, using a heating element which remains embedded. More particularly, the invention relates to thermoplastic welding through resistance heating for effecting a welding bond over relatively large surface areas of the parts to be joined through these areas. Preferably, the invention is practiced for welding a saddle flange to the surface of a thermoplastic tube.
Various heating elements for effecting a welding bond between thermoplastics have become known. These elements are usually comprised of one or several metallic wires for resistance heating. The wire or wires are disposed between the plastic parts. Upon feeding current to the wire or wires, the plastic material softens and liquifies, and fuses as to the different parts which, thereupon, are bonded rather homogenically. The resistance elements remains embedded in the plastic.
The known heating elements of that type are usually suitable only in welding sleeves or for local welding of parts, more or less equivalent to spot or seam welding. They are not well suited for providing a large area contact between two parts which engage each other over relatively large surface portions.